Unsaturated polyester resins are typically used together with a reactive diluent, usually a volatile unsaturated organic monomer, which is generally referred to as a reactive diluent. The unsaturated organic monomer copolymerizes with the polyester resins to form a gelcoating and may be used in other applications such as pultrusion, resin lamination, sheet molding compounding, bulk molding compounding, etc.
During curing some of the volatile organic monomer is lost to the atmosphere. Due to environmental concerns of such organic compounds, legislation has been passed which requires reduction in the amount of volatile organic compounds which may be released to the atmosphere.
One method of reducing such VOC emission is replacement of the reactive diluent with a less volatile reactive diluent. However, this approach has led to slower curing times and/or incomplete curing at normal ambient temperatures. Another approach is the reduction in the amount of reactive diluent. This approach has led to increases in viscosity beyond useable values. If viscosity increase is compensated by use of a lower molecular weight polyester, then poor final gelcoat properties have resulted. Another approach has been the use of a suppressant which reduces the loss of VOCs. The suppressants are often waxes which lead to a reduction in interlaminar adhesion of the gelcoat. It is desirable to have a gelcoat product which has reduced VOC and also which has acceptable gel time and good final gelcoat properties.